Semiconductor constructions comprising three-dimensional thin film transistor devices and resistors

ABSTRACT

The invention includes semiconductor constructions having a thin film stacked resistor in electrical connection with a source/drain region of a transistor device. The resistor includes first and second crystalline layers which may or may not differ from one another. One of the first and second crystalline layers comprises doped silicon/germanium, and the other comprises doped silicon. The transistor device and resistor can be part of an SOI construction formed over a conventional substrate (such as a monocrystalline silicon wafer) or a non-conventional substrate (such as one or more of glass, aluminum oxide, silicon dioxide, metal and plastic). The invention also includes processes of forming semiconductor constructions, and in particular aspects, includes processes of forming resistor constructions.

TECHNICAL FIELD

The invention pertains to semiconductor constructions comprising transistors and resistors; and also pertains to methods of forming semiconductor constructions. In particular aspects, the invention pertains to processes of forming resistor constructions.

BACKGROUND OF THE INVENTION

SOI technology differs from traditional bulk semiconductor technologies in that the active semiconductor material of SOI technologies is typically much thinner than that utilized in bulk technologies. The active semiconductor material of SOI technologies will typically be formed as a thin film over an insulating material (typically oxide), with exemplary thicknesses of the semiconductor film being less than or equal to 2000 Å. In contrast, bulk semiconductor material will typically have a thickness of at least about 200 microns. The thin semiconductor of SOI technology can allow higher performance and lower power consumption to be achieved in integrated circuits than can be achieved with similar circuits utilizing bulk materials.

An exemplary integrated circuit device that can be formed utilizing SOI technologies is a so-called thin film transistor (TFT), with the term “thin film” referring to the thin semiconductor film of the SOI construction. In particular aspects, the semiconductor material of the SOI construction can be silicon, and in such aspects the TFTs can be fabricated using recrystallized amorphous silicon or polycrystalline silicon. The silicon can be supported by an electrically insulative material (such as silicon dioxide), which in turn is supported by an appropriate substrate. Exemplary substrate materials include glass, bulk silicon and metal-oxides (such as, for example, Al₂O₃). If the semiconductor material comprises silicon, the term SOI is occasionally utilized to refer to a silicon-on-insulator construction, rather than the more general concept of a semiconductor-on-insulator construction. However, it is to be understood that in the context of this disclosure the term SOI refers to semiconductor-on-insulator constructions. Accordingly, the semiconductor material of an SOI construction referred to in the context of this disclosure can comprise other semiconductive materials in addition to, or alternatively to, silicon; including, for example, germanium.

A problem associated with conventional TFT constructions is that grain boundaries and defects can limit carrier mobilities. Accordingly, carrier mobilities are frequently nearly an order of magnitude lower than they would be in bulk semiconductor devices. High voltage (and therefore high power consumption), and large areas are utilized for the TFTs, and the TFTs exhibit limited performance. TFTs thus have limited commercial application and currently are utilized primarily for large area electronics.

Various efforts have been made to improve carrier mobility of TFTs. Some improvement is obtained for devices in which silicon is the semiconductor material by utilizing a thermal anneal for grain growth following silicon ion implantation and hydrogen passivation of grain boundaries (see, for example, Yamauchi, N. et al., “Drastically Improved Performance in Poly-Si TFTs with Channel Dimensions Comparable to Grain Size”, IEDM Tech. Digest, 1989, pp. 353-356). Improvements have also been made in devices in which a combination of silicon and germanium is the semiconductor material by optimizing the germanium and hydrogen content of silicon/germanium films (see, for example, King, T. J. et al, “A Low-Temperature (<=550° C.) Silicon-Germanium MOS TFT Technology for Large-Area Electronics”, IEDM Tech. Digest, 1991, pp. 567-570).

Investigations have shown that nucleation, direction of solidification, and grain growth of silicon crystals can be controlled selectively and preferentially by excimer laser annealing, as well as by lateral scanning continuous wave laser irradiation/anneal for recrystallization (see, for example, Kuriyama, H. et al., “High Mobility Poly-Si TFT by a New Excimer Laser Annealing Method for Large Area Electronics”, IEDM Tech. Digest, 1991, pp. 563-566; Jeon, J. H. et al., “A New Poly-Si TFT with Selectively Doped Channel Fabricated by Novel Excimer Laser Annealing”, IEDM Tech. Digest, 2000, pp. 213-216; Kim, C. H. et al., “A New High-Performance Poly-Si TFT by Simple Excimer Laser Annealing on Selectively Floating a Si Layer”, IEDM Tech. Digest, 2001, pp. 753-756; Hara, A. et al, “Selective Single-Crystalline-Silicon Growth at the Pre-Defined Active Regions of TFTs on a Glass by a Scanning CW Layer Irradiation”, IEDM Tech. Digest, 2000, pp. 209-212; and Hara, A. et al., “High Performance Poly-Si TFTs on a Glass by a Stable Scanning CW Laser Lateral Crystallization”, IEDM Tech. Digest, 2001, pp. 747-750). Such techniques have allowed relatively defect-free large crystals to be grown, with resulting TFTs shown to exhibit carrier mobility over 300 cm²/V-second.

Another technique which has shown promise for improving carrier mobility is metal-induced lateral recrystallization (MILC), which can be utilized in conjunction with an appropriate high temperature anneal (see, for example, Jagar, S. et al., “Single Grain TFT with SOI CMOS Performance Formed by Metal-Induced-Lateral-Crystallization”, IEDM Tech. Digest, 1999, p. 293-296; and Gu, J. et al., “High Performance Sub-100 nm Si TFT by Pattern-Controlled Crystallization of Thin Channel Layer and High Temperature Annealing”, DRC Conference Digest, 2002, pp. 49-50). A suitable post-recrystallization anneal for improving the film quality within silicon recrystallized by MILC is accomplished by exposing recrystallized material to a temperature of from about 850° C. to about 900° C. under an inert ambient (with a suitable ambient comprising, for example, N₂). MILC can allow nearly single crystal silicon grains to be formed in predefined amorphous-silicon islands for device channel regions. Nickel-induced-lateral-recrystallization can allow device properties to approach those of single crystal silicon.

The carrier mobility of a transistor channel region can be significantly enhanced if the channel region is made of a semiconductor material having a strained crystalline lattice (such as, for example, a silicon/germanium material having a strained lattice, or a silicon material having a strained lattice) formed over a semiconductor material having a relaxed lattice (such as, for example, a silicon/germanium material having a relaxed crystalline lattice). (See, for example, Rim, K. et al., “Strained Si NMOSFETs for High Performance CMOS Technology”, VLSI Tech. Digest, 2001, p. 59-60; Cheng, Z. et al., “SiGe-On-Insulator (SGOI) Substrate Preparation and MOSFET Fabrication for Electron Mobility Evaluation” 2001 IEEE SOI Conference Digest, October 2001, pp. 13-14; Huang, L. J. et al., “Carrier Mobility Enhancement in Strained Si-on-Insulator Fabricated by Wafer Bonding”, VLSI Tech. Digest, 2001, pp. 57-58; and Mizuno, T. et al., “High Performance CMOS Operation of Strained-SOI MOSFETs Using Thin Film SiGe-on-Insulator Substrate”, VLSI Tech. Digest, 2002, p. 106-107.)

The terms “relaxed crystalline lattice” and “strained crystalline lattice” are utilized to refer to crystalline lattices which are within a defined lattice configuration for the semiconductor material, or perturbed from the defined lattice configuration, respectively. In applications in which the relaxed lattice material comprises silicon/germanium having a germanium concentration of from 10% to 60%, mobility enhancements of 110% for electrons and 60-80% for holes can be accomplished by utilizing a strained lattice material in combination with the relaxed lattice material (see for example, Rim, K. et al., “Characteristics and Device Design of Sub-100 nm Strained SiN and PMOSFETs”, VLSI Tech. Digest, 2002, 00. 98-99; and Huang, L. J. et al., “Carrier Mobility Enhancement in Strained Si-on-Insulator Fabricated by Wafer Bonding”, VLSI Tech. Digest, 2001, pp. 57-58).

Performance enhancements of standard field effect transistor devices are becoming limited with progressive lithographic scaling in conventional applications. Accordingly, strained-lattice-channeled-field effect transistors on relaxed silicon/germanium offers an opportunity to enhance device performance beyond that achieved through conventional lithographic scaling. IBM recently announced the world's fastest communications chip following the approach of utilizing a strained crystalline lattice over a relaxed crystalline lattice (see, for example, “IBM Builds World's Fastest Communications Microchip”, Reuters U.S. Company News, Feb. 25, 2002; and Markoff, J., “IBM Circuits are Now Faster and Reduce Use of Power”, The New York Times, Feb. 25, 2002).

Although various techniques have been developed for substantially controlling nucleation and grain growth processes of semiconductor materials, grain orientation control is lacking. Further, the post-anneal treatment utilized in conjunction with MILC can be unsuitable in applications in which a low thermal budget is desired. Among the advantages of the invention described below is that such can allow substantial control of crystal grain orientation within a semiconductor material, while lowering thermal budget requirements relative to conventional methods. Additionally, the quality of the grown crystal formed from a semiconductor material can be improved relative to that of conventional methods.

Field effect transistor devices can be utilized in various types of circuitry. For instance, field effect transistor devices can be incorporated into transistor/resistor constructions. FIG. 1 shows a schematic diagram of a construction 2 comprising a transistor 4 and a resistor 6. The transistor has one source/drain region extending through the resistor to V_(DD) potential, and has another source/drain region at ground potential. The gate of the transistor is tied to an electrical node 8 which controls potential and/or current flow at the gate.

Transistors and resistors are common components of semiconductor circuitry. A continuing goal in fabrication of semiconductor circuitry is to increase a density of the circuitry. Accordingly, there is a continuing goal to reduce the footprint associated with transistor/resistor constructions, while maintaining desired performance characteristics of the constructions.

SUMMARY OF THE INVENTION

In one aspect, the invention pertains to a semiconductor construction comprising a transistor device and a resistor. The transistor device includes a gate and an active region proximate the gate. The active region comprises a pair of source/drain regions. A resistor is in electrical connection with one of the source/drain regions. The resistor comprises a first crystalline layer and a second crystalline layer over the first crystalline layer. The second crystalline layer has a different composition than the first crystalline layer. The second crystalline layer comprises doped silicon/germanium and the first crystalline layer comprises doped silicon. The transistor device and resistor can be part of an SOI construction formed over a conventional substrate (such as a monocrystalline silicon wafer) or a non-conventional substrate (such as one or more of glass, aluminum oxide, silicon dioxide, metal and plastic).

In another aspect, the invention encompasses a process of forming a resistor construction. A first crystalline layer is formed over a substrate. The first crystalline layer comprises one or more silicon seed crystals. A second crystalline layer is formed over the first crystalline layer. The second crystalline comprises Si/Ge. The first and second layers together are comprised by a resistor which extends between a first electrical node and a second electrical node.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below with reference to the following accompanying drawings.

FIG. 1 is a schematic diagram of a prior art construction comprising a transistor and resistor.

FIG. 2 is a diagrammatic, cross-sectional view of a fragment of a semiconductor construction shown at a preliminary stage of an exemplary process of the present invention

FIG. 3 is a view of the FIG. 2 wafer shown at a processing stage subsequent to that of FIG. 2.

FIG. 4 is a view of the FIG. 2 fragment shown at a processing stage subsequent to that of FIG. 3.

FIG. 5 is a view of the FIG. 2 fragment shown at a processing stage subsequent to that of FIG. 4.

FIG. 6 is a view of the FIG. 2 fragment shown at a processing stage subsequent to that of FIG. 5.

FIG. 7 is a view of the FIG. 2 fragment shown at a processing stage subsequent to that of FIG. 6.

FIG. 8 is an expanded region of the FIG. 7 fragment shown at a processing stage subsequent to that of FIG. 7 in accordance with an exemplary embodiment of the present invention.

FIG. 9 is a view of the FIG. 8 fragment shown at a processing stage subsequent to that of FIG. 8.

FIG. 10 is a view of an expanded region of FIG. 7 shown at a processing stage subsequent to that of FIG. 7 in accordance with an alternative embodiment relative to that of FIG. 8.

FIG. 11 is a diagrammatic, cross-sectional view of a semiconductor fragment illustrating an exemplary semiconductor construction comprising a transistor and resistor.

FIG. 12 is a top cross-sectional view along the line 12—12 of the construction comprising the FIG. 11 fragment. The FIG. 11 cross-section is along the line 11—11 of FIG. 12.

FIG. 13 is a diagrammatic view of a computer illustrating an exemplary application of the present invention.

FIG. 14 is a block diagram showing particular features of the motherboard of the FIG. 13 computer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An exemplary method of forming an SOI construction in accordance with an aspect of the present invention is described with reference to FIGS. 2-7.

Referring initially to FIG. 2, a fragment of a semiconductor construction 10 is illustrated at a preliminary processing stage. To aid in interpretation of the claims that follow, the terms “semiconductive substrate” and “semiconductor substrate” are defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.

Construction 10 comprises a base (or substrate) 12 and an insulator layer 14 over the base. Base 12 can comprise, for example, one or more of glass, aluminum oxide, silicon dioxide, metal and plastic. Additionally, and/or alternatively, base 12 can comprise a semiconductor material, such as, for example, a silicon wafer.

Layer 14 comprises an electrically insulative material, and in particular applications can comprise, consist essentially of, or consist of silicon dioxide. In the shown construction, insulator layer 14 is in physical contact with base 12. It is to be understood, however, that there can be intervening materials and layers provided between base 12 and layer 14 in other aspects of the invention (not shown). For example, a chemically passive thermally stable material, such as silicon nitride (Si₃N₄), can be incorporated between base 12 and layer 14. Layer 14 can have a thickness of, for example, from about 200 nanometers to about 500 nanometers, and can be referred to as a buffer layer.

Layer 14 preferably has a planarized upper surface. The planarized upper surface can be formed by, for example, chemical-mechanical polishing.

A layer 16 of semiconductive material is provided over insulator layer 14. In the shown embodiment, semiconductive material layer 16 is formed in physical contact with insulator 14. Layer 16 can have a thickness of, for example, from about 5 nanometers to about 10 nanometers. Layer 16 can, for example, comprise, consist essentially of, or consist of either doped or undoped silicon. If layer 16 comprises, consists essentially of, or consists of doped silicon, the dopant concentration can be from about 10¹⁴ atoms/cm³ to about 10²⁰ atoms/cm³. The dopant can be either n-type or p-type, or a combination of n-type and p-type.

The silicon utilized in layer 16 can be either polycrystalline silicon or amorphous silicon at the processing stage of FIG. 2. It can be advantageous to utilize amorphous silicon in that it is typically easier to deposit a uniform layer of amorphous silicon than to deposit a uniform layer of polycrystalline silicon.

Referring to FIG. 3, material 16 is patterned into a plurality of discrete islands (or blocks) 18. Such can be accomplished utilizing, for example, photoresist (not shown) and photolithographic processing, together with an appropriate etch of material 16.

A capping layer 20 is provided over islands 18 and over portions of layer 14 exposed between the islands. Layer 20 can, for example, comprise, consist essentially of, or consist of one or both of silicon dioxide and silicon. Layer 20 can also comprise multiple layers of silicon dioxide, stress-free silicon oxynitride, and silicon.

After formation of capping layer 20, small voids (nanovoids) and small crystals are formed in the islands 18. The formation of the voids and crystals can be accomplished by ion implanting helium 22 into material 16 and subsequently exposing material 16 to laser-emitted electromagnetic radiation. The helium can aid in formation of the nanovoids; and the nanovoids can in turn aid in crystallization and stress relief within the material 16 during exposure to the electromagnetic radiation. The helium can thus allow crystallization to occur at lower thermal budgets than can be achieved without the helium implantation. The helium is preferably implanted selectively into islands 18 and not into regions between the islands. The exposure of construction 10 to electromagnetic radiation can comprise subjecting the construction to scanned continuous wave laser irradiation while the construction is held at an appropriate elevated temperature (typically from about 300° C. to about 450° C.). The exposure to the electromagnetic radiation can complete formation of single crystal seeds within islands 18. The laser irradiation is scanned along an axis 24 in the exemplary shown embodiment.

The capping layer 20 discussed previously is optional, but can beneficially assist in retaining helium within islands 18 and/or preventing undesirable impurity contamination during the treatment with the laser irradiation.

Referring to FIG. 4, islands 18 are illustrated after voids have been formed therein. Additionally, small crystals (not shown) have also been formed within islands 18 as discussed above.

Capping layer 20 (FIG. 3) is removed, and subsequently a layer 26 of semiconductive material is formed over islands 18. Layer 26 can comprise, consist essentially of, or consist of silicon and germanium; or alternatively can comprise, consist essentially of, or consist of doped silicon/germanium. The germanium concentration within layer 26 can be, for example, from about 10 atomic percent to about 60 atomic percent. In the shown embodiment, layer 26 physically contacts islands 18, and also physically contacts insulator layer 14 in gaps between the islands. Layer 26 can be formed to a thickness of, for example, from about 50 nanometers to about 100 nanometers, and can be formed utilizing a suitable deposition method, such as, for example, plasma-assisted chemical vapor deposition.

A capping layer 28 is formed over semiconductor layer 26. Capping layer 28 can comprise, for example, silicon dioxide. Alternatively, capping layer 28 can comprise, for example, a combination of silicon dioxide and stress-free silicon oxynitride. Capping layer 28 can protect a surface of layer 26 from particles and contaminants that could otherwise fall on layer 26. If the processing of construction 10 occurs in an environment in which particle formation and/or incorporation of contaminants is unlikely (for example, an ultrahigh vacuum environment), layer 28 can be eliminated from the process. Layer 28 is utilized in the patterning of a metal (discussed below). If layer 28 is eliminated from the process, other methods besides those discussed specifically herein can be utilized for patterning the metal.

Referring to FIG. 5, openings 30 are extended through capping layer 28 and to an upper surface of semiconductive material 26. Openings 30 can be formed by, for example, photolithographic processing to pattern a layer of photoresist (not shown) into a mask, followed by a suitable etch of layer 28 and subsequent removal of the photoresist mask.

A layer 32 of metal-containing material is provided within openings 30, and in physical contact with an upper surface of semiconductive material 26. Layer 32 can have a thickness of, for example, less than or equal to about 10 nanometers. The material of layer 32 can comprise, consist essentially of, or consist of, for example, nickel. Layer 32 can be formed by, for example, physical vapor deposition. Layer 32 can be formed to be within openings 30 and not over material 28 (as is illustrated in FIG. 5) by utilizing deposition conditions which selectively form metal-containing layer 32 on a surface of material 26 relative to a surface of material 28. Alternatively, material 32 can be deposited by a substantially non-selective process to form the material 32 over the surface of material 28 as well as over the surface of material 26 within openings 30, and subsequently material 32 can be selectively removed from over surfaces of material 28 while remaining within openings 30. Such selective removal can be accomplished by, for example, chemical-mechanical polishing, and/or by forming a photoresist mask (not shown) over the material 32 within openings 30, while leaving other portions of material 32 exposed, and subsequently removing such other portions to leave only the segments of material 32 within openings 30. The photoresist mask can then be removed.

Oxygen 34 is ion implanted through layers 26 and 28, and into layer 16 to oxidize the material of layer 16. For instance, if layer 16 consists of silicon, the oxygen can convert the silicon to silicon dioxide. Such swells the material of layer 16, and accordingly fills the nanovoids that had been formed earlier. The oxygen preferably only partially oxidizes layer 16, with the oxidation being sufficient to fill all, or at least substantially all, of the nanovoids; but leaving at least some of the seed crystals within layer 16 that had been formed with the laser irradiation discussed previously. In some aspects, the oxidation can convert a lower portion of material 16 to silicon dioxide while leaving an upper portion of material 16 as non-oxidized silicon.

The oxygen ion utilized as implant 34 can comprise, for example, oxygen (O₂) or ozone (O₃). The oxygen ion implant can occur before or after formation of openings 30 and provision of metal-containing layer 32.

Construction 10 is exposed to continuous wave laser irradiation while being held at an appropriate temperature (which can be, for example, from about 300° C. to about 450° C.; or in particular applications can be greater than or equal to 550° C.) to cause transformation of at least some of layer 26 to a crystalline form. The exposure to the laser irradiation comprises exposing the material of construction 10 to laser-emitted electromagnetic radiation scanned along a shown axis 36. Preferably, the axis 36 along which the laser irradiation is scanned is the same axis that was utilized for scanning of laser irradiation in the processing stage of FIG. 3.

The crystallization of material 26 (which can also be referred to as a recrystallization of the material) is induced utilizing metal-containing layer 32, and accordingly corresponds to an application of MILC. The MILC transforms material 26 to a crystalline form and the seed layer provides the crystallographic orientation while undergoing partial oxidation.

The crystal orientation within crystallized layer 26 can originate from the crystals initially formed in islands 18. Accordingly, crystal orientations formed within layer 26 can be controlled through control of the crystal orientations formed within the semiconductive material 16 of islands 18.

The oxidation of part of material 16 which was described previously can occur simultaneously with the MILC arising from continuous wave laser irradiation. Partial oxidation of seed layer 16 facilitates: (1) Ge enrichment into Si—Ge layer 26 (which improves carrier mobility); (2) stress-relief of Si—Ge layer 26; and (3) enhancement of recrystallization of Si—Ge layer 26. The crystallization of material 26 can be followed by an anneal of material 26 at a temperature of, for example, about 900° C. for a time of about 30 minutes, or by an appropriate rapid thermal anneal, to further ensure relaxed, defect-free crystallization of material 26.

FIG. 6 shows construction 10 after the processing described above with reference to FIG. 5. Specifically, the voids that had been in material 16 are absent due to the oxidation of material 16. Also, semiconductive material 26 has been transformed into a crystalline material (illustrated diagrammatically by the cross-hatching of material 26 in FIG. 6). Crystalline material 26 can consist of a single large crystal, and accordingly can be monocrystalline. Alternatively, crystalline material 26 can be polycrystalline. If crystalline material 26 is polycrystalline, the crystals of the material will preferably be equal in size or larger than the blocks 18. In particular aspects, each crystal of the polycrystalline material can be about as large as one of the shown islands 18. Accordingly, the islands can be associated in a one-to-one correspondence with crystals of the polycrystalline material.

The shown metal layers 32 are effectively in a one-to-one relationship with islands 18, and such one-to-one correspondence of crystals to islands can occur during the MILC. Specifically, single crystals can be generated relative to each of islands 18 during the MILC process described with reference to FIG. 5. It is also noted, however, that although the metal layers 32 are shown in a one-to-one relationship with the islands in the cross-sectional views of FIGS. 5 and 6, the construction 10 comprising the shown fragment should be understood to extend three dimensionally. Accordingly, the islands 18 and metal layers 32 can extend in directions corresponding to locations into and out of the page relative to the shown cross-sectional view. There can be regions of the construction which are not shown where a metal layer overlaps with additional islands besides the shown islands.

Referring to FIG. 7, layers 28 and 32 (FIG. 6) are removed, and subsequently a layer 40 of crystalline semiconductive material is formed over layer 26. In typical applications, layer 26 will have a relaxed crystalline lattice and layer 40 will have a strained crystalline lattice. As discussed previously, layer 26 will typically comprise both silicon and germanium, with the germanium being present to a concentration of from about 10 atomic percent to about 60 atomic percent. Layer 40 can comprise, consist essentially of, or consist of either doped or undoped silicon; or alternatively can comprise, consist essentially of, or consist of either doped or undoped silicon/germanium. If layer 40 comprises silicon/germanium, the germanium content can be from about 10 atomic percent to about 60 atomic percent.

Strained lattice layer 40 can be formed by utilizing methods similar to those described in, for example, Huang, L. J. et al., “Carrier Mobility Enhancement in Strained Si-on-Insulator Fabricated by Wafer Bonding”, VLSI Tech. Digest, 2001, pp. 57-58; and Cheng, Z. et al., “SiGe-On-Insulator (SGOI) Substrate Preparation and MOSFET Fabrication for Electron Mobility Evaluation” 2001 IEEE SOI Conference Digest, October 2001, pp. 13-14.

Strained lattice layer 40 can be large polycrystalline or monocrystalline. If strained lattice layer 40 is polycrystalline, the crystals of layer 40 can be large and in a one-to-one relationship with the large crystals of a polycrystalline relaxed crystalline layer 26. Strained lattice layer 40 is preferably monocrystalline over the individual blocks 18.

The strained crystalline lattice of layer 40 can improve mobility of carriers relative to the material 26 having a relaxed crystalline lattice. However, it is to be understood that layer 40 is optional in various aspects of the invention.

Each of islands 18 can be considered to be associated with a separate active region 42, 44 and 46. The active regions can be separated from one another by insulative material subsequently formed through layers 26 and 40 (not shown). For instance, a trenched isolation region can be formed through layers 26 and 40 by initially forming a trench extending through layers 26 and 40 to insulative material 14, and subsequently filling the trench with an appropriate insulative material such as, for example, silicon dioxide.

As discussed previously, crystalline material 26 can be a single crystal extending across an entirety of the construction 10 comprising the shown fragment, and accordingly extending across all of the shown active regions. Alternatively, crystalline material 26 can be polycrystalline. If crystalline material 26 is polycrystalline, the single crystals of the polycrystalline material will preferably be large enough so that only one single crystal extends across a given active region. In other words, active region 42 will preferably comprise a single crystal of material 26, active region 44 will comprise a single crystal of the material, and active region 46 will comprise a single crystal of the material, with the single crystals being separate and discrete relative to one another.

FIG. 8 shows an expanded view of active region 44 at a processing stage subsequent to that of FIG. 7, and specifically shows a transistor device 50 associated with active region 44 and supported by crystalline material 26.

Transistor device 50 comprises a dielectric material 52 formed over strained lattice 40, and a gate 54 formed over dielectric material 52. Dielectric material 52 typically comprises silicon dioxide, and gate 54 typically comprises a stack including an appropriate conductive material, such as, for example, conductively-doped silicon and/or metal.

A channel region 56 is beneath gate 54, and in the shown construction extends across strained crystalline lattice material 40. The channel region may also extend into relaxed crystalline lattice material 26 (as shown). Channel region 56 is doped with a p-type dopant.

Transistor construction 50 additionally comprises source/drain regions 58 which are separated from one another by channel region 56, and which are doped with n-type dopant to an n⁺ concentration (typically, a concentration of at least 10²¹ atoms/cm³). In the shown construction, source/drain regions 58 extend across strained lattice layer 40 and into relaxed lattice material 26. Although source/drain regions 58 are shown extending only partially through relaxed lattice layer 26, it is to be understood that the invention encompasses other embodiments (not shown) in which the source/drain regions extend all the way through relaxed material 26 and to material 16.

Channel region 56 and source/drain regions 58 can be formed by implanting the appropriate dopants into crystalline materials 26 and 40. The dopants can be activated by rapid thermal activation (RTA), which can aid in keeping the thermal budget low for fabrication of field effect transistor 50.

An active region of transistor device 50 extends across source/drain regions 58 and channel region 56. Preferably the portion of the active region within crystalline material 26 is associated with only one single crystal of material 26. Such can be accomplished by having material 26 be entirely monocrystalline. Alternatively, material 26 can be polycrystalline and comprise an individual single grain which accommodates the entire portion of the active region that is within material 26. The portion of strained lattice material 40 that is encompassed by the active region is preferably a single crystal, and can, in particular aspects, be considered an extension of the single crystal of the relaxed lattice material 26 of the active region.

Crystalline materials 40 and 26 can, together with any crystalline structures remaining in material 16, have a total thickness of less than or equal to about 2000 Å. Accordingly the crystalline material can correspond to a thin film formed over an insulative material. The insulative material can be considered to be insulative layer 14 alone, or a combination of insulative layer 14 and oxidized portions of material 16.

The transistor structure 50 of FIG. 8 corresponds to an n-type field effect transistor (NFET), and in such construction it can be advantageous to have strained crystalline material 40 consist of a strained silicon material having appropriate dopants therein. The strained silicon material can improve mobility of electrons through channel region 56, which can improve performance of the NFET device relative to a device lacking the strained silicon lattice. Although it can be preferred that strained lattice material 40 comprise silicon in an NFET device, it is to be understood that the strained lattice can also comprise other semiconductive materials. A strained silicon lattice can be formed by various methods. For instance, strained silicon could be developed by various means and lattice 40 could be created by lattice mismatch with other materials or by geometric conformal lattice straining on another substrate (mechanical stress).

As mentioned above, strained lattice 40 can comprise other materials alternatively to, or additionally to, silicon. The strained lattice can, for example, comprise a combination of silicon and germanium. There can be advantages to utilizing the strained crystalline lattice comprising silicon and germanium relative to structures lacking any strained lattice. However, it is generally most preferable if the strained lattice consists of silicon alone (or doped silicon), rather than a combination of silicon and germanium for an NFET device.

A pair of sidewall spacers 60 are shown formed along sidewalls of gate 54, and an insulative mass 62 is shown extending over gate 54 and material 40. Conductive interconnects 63 and 64 extend through the insulative mass 62 to electrically connect with source/drain regions 58. Interconnects 63 and 64 can be utilized for electrically connecting transistor construction 50 with other circuitry external to transistor construction 50. Such other circuitry can include, for example, a bitline and a capacitor in applications in which construction 50 is incorporated into dynamic random access memory (DRAM).

FIG. 9 shows construction 10 at a processing stage subsequent to that of FIG. 8, and shows a capacitor structure 100 formed over and in electrical contact with conductive interconnect 64. The shown capacitor structure extends across gate 54 and interconnect 63.

Capacitor construction 100 comprises a first capacitor electrode 102, a second capacitor electrode 104, and a dielectric material 106 between capacitor electrodes 102 and 104. Capacitor electrodes 102 and 104 can comprise any appropriate conductive material, including, for example, conductively-doped silicon. In particular aspects, electrodes 102 and 104 will each comprise n-type doped silicon, such as, for example, polycrystalline silicon doped to a concentration of at least about 10²¹ atoms/cm³ with n-type dopant. In a particular aspect of the invention, electrode 102, conductive interconnect 64 and the source/drain region 58 electrically connected with interconnect 64 comprise, or consist of, n-type doped semiconductive material. Accordingly, n-type doped semiconductive material extends from the source/drain region, through the interconnect, and through the capacitor electrode.

Dielectric material 106 can comprise any suitable material, or combination of materials. Exemplary materials suitable for dielectric 106 are high dielectric constant materials including, for example, silicon nitride, aluminum oxide, TiO₂, Ta₂O₅, ZrO₂, etc.

The conductive interconnect 63 is in electrical connection with a bitline 108. Top capacitor electrode 104 is shown in electrical connection with an interconnect 110, which in turn connects with a reference voltage 112, which can, in particular aspects, be ground. The construction of FIG. 9 can be considered a DRAM cell, and such can be incorporated into a computer system as a memory device.

FIG. 10 shows construction 10 at a processing stage subsequent to that of FIG. 7 and alternative to that described previously with reference to FIG. 8. In referring to FIG. 10, similar numbering will be used as is used above in describing FIG. 8, where appropriate.

A transistor construction 70 is shown in FIG. 10, and such construction differs from the construction 50 described above with reference to FIG. 8 in that construction 70 is a p-type field effect transistor (PFET) rather than the NFET of FIG. 8. Transistor device 70 comprises an n-type doped channel region 72 and p⁺-doped source/drain regions 74. In other words, the channel region and source/drain regions of transistor device 70 are oppositely doped relative to the channel region and source/drain regions described above with reference to the NFET device 50 of FIG. 8.

The strained crystalline lattice material 40 of the PFET device 70 can consist of appropriately doped silicon, or consist of appropriately doped silicon/germanium. It can be most advantageous if the strained crystalline lattice material 40 comprises appropriately doped silicon/germanium in a PFET construction, in that silicon/germanium can be a more effective carrier of holes with higher mobility than is silicon without germanium.

The transistor devices discussed above (NFET device 50 of FIG. 8, and PFET device 70 of FIG. 10) can be utilized in numerous constructions in addition to the construction described above with reference to FIG. 9. Another exemplary construction is described with reference to FIGS. 11 and 12.

FIGS. 11 and 12 show a semiconductor construction 100 comprising a substrate 102 having an insulative layer 104 formed thereover. Substrate 102 and insulative layer 104 can comprise, for example, the materials described previously with reference to substrate 12 and insulator layer 14, respectively. Accordingly, substrate 102 can comprise, for example, one or more of glass, aluminum oxide, silicon dioxide, metal, semiconductor material and plastic. Layer 104 can comprise any suitable electrically insulative material, including, for example, silicon dioxide. Layer 104 can be formed physically against substrate 102, or can be separated from substrate 102 by one or more intervening materials, including, for example, a chemically passive thermally stable material, such as silicon nitride.

A first crystalline layer 106, second crystalline layer 108, and third crystalline layer 110 are formed over insulative material 104. Layers 106, 108 and 110 can correspond to a silicon seed layer, relaxed crystalline lattice layer, and strained crystalline lattice layer, respectively. In particular aspects, layers 106, 108 and 110 can comprise materials described previously for layers 16, 26 and 40, respectively, of FIGS. 2-7. Accordingly, layer 108 can comprise relaxed silicon/germanium; with the germanium being present to from about 10 atomic % to about 60 atomic %. Layer 110 can comprise, consist essentially of, or consist of doped strained silicon; or alternatively can comprise, consist essentially of, or consist of doped strained or unstrained silicon/germanium. Layer 106 can comprise, consist essentially of, or consist of doped silicon.

A dielectric material 112 is over layer 110, and a transistor gate 114 is over dielectric material 112. Dielectric material 112 can comprise, consist essentially of, or consist of silicon dioxide. Transistor gate 114 can comprise, for example, one or more of metal and conductively-doped silicon; and can, for example, comprise materials described previously with reference to transistor gate 54 of FIGS. 8-10.

A pair of source/drain regions 116 extend through strained crystalline lattice layer 110 and into relaxed crystalline lattice layer 108. The source/drain regions comprise a shallow portion 118, and a deeper portion 120. Such shape of the source/drain regions can be accomplished utilizing a first shallow implant, followed by formation of sidewall spacers (not shown) along sidewalls of gate 114, and a subsequent deep implant of n-type material. The sidewall spacers can then be removed to leave the resulting structure shown in FIG. 11. Alternatively, the sidewall spacers can be left in place to form a structure similar to that of FIG. 8 (with the sidewall spacers of FIG. 8 being labeled as 60).

A channel region 122 extends beneath gate 114, and between source/drain regions 116. An NFET transistor device comprises gate 114, source/drain regions 116 and channel region 122. Although the shown transistor device is an NFET device, it is to be understood that the invention encompasses other aspects (not shown) in which the transistor device is a PFET device.

Source/drain regions 116 and channel region 122 define an active region of the transistor device. For reasons described previously, it can be advantageous to have the entirety of the portion of the active region within layer 108 contained within a single crystal of the crystalline material of layer 108; and it can also be advantageous to have the entirety of the portion of the active region within layer 110 contained within a single crystal of the material 110. Also, although the source/drain regions are shown terminating above layer 106, it is to be understood that the invention encompasses other aspects (not shown) in which the source/drain regions extend into layer 106. In such aspects, it can be advantageous if the entirety of the portion of the active region within layer 106 is contained within a single crystal of material 106.

The crystalline materials of layers 106, 108 and 110 can be monocrystalline in order that an entirety of the active region within such crystalline materials is within single crystals of the materials. Alternatively, the materials can be polycrystalline, with individual single crystals being large enough to accommodate an entirety of the portion of the active region extending within the various materials. In particular aspects, layers 108 and 110 will be extensions of a crystalline lattice defined by material 106. In such aspects, an entirety of the active region of the transistor device will preferably extend within only a single crystal encompassing materials 106, 108 and 110.

A conductive pillar 130 is formed in electrical connection with one of the source/drain regions 116. In the shown embodiment, pillar 130 comprises n-type doped silicon, and is formed in physical contact with an upper surface of layer 110. The material of pillar 130 can be formed by, for example, selective epitaxial growth of semiconductive material over layer 110. The material of pillar 130 can subsequently be doped by out-diffusion of dopant from source/drain region 116 into the semiconductive material of pillar 130, or alternatively by ion implantation.

A pair of crystalline materials 132 and 134 are formed over pillar 130. In alternative embodiments, layers 132 and 134 can be replaced with a single layer (not shown). In aspects in which pillar 130 comprises a crystalline semiconductive material, layers 132 and 134 can be formed by epitaxial growth over the semiconductive material of pillar 130, and/or by one or more techniques discussed previously with reference to FIGS. 5-7. In the shown aspect of the invention, pillar 130 comprises an upper surface 131, and layer 132 is formed physically against such upper surface.

An electrical node 136 is formed at a location distant from conductive pillar 130, and crystalline materials 132 and 134 extend between node 136 and pillar 130. Crystalline materials 132 and 134 together define a resistor 135 extending between a first electrical node defined by pillar 130, and a second electrical node defined by the shown node 136. Node 136 can comprise any suitable conductive material, including, a suitably doped semiconductive material. In the shown embodiment, node 136 comprises n-type doped semiconductive material. Such semiconductive material can be, for example, silicon, and can be in a monocrystalline, polycrystalline, or amorphous form.

Crystalline materials 132 and 134 may or may not comprise different compositions from one another. Crystalline material 132 can comprise, consist essentially of, or consist of p-type doped silicon; and crystalline material 134 can comprise, consist essentially of, or consist of p-type doped silicon/germanium. Alternatively, the two layers can be replaced with a single layer of either p-doped silicon or p-doped silicon/germanium.

If crystalline material 134 comprises p-type doped silicon/germanium, the germanium content can be, for example, from about 10 atomic % to about 60 atomic %. Crystalline materials 132 and 134 can be polycrystalline, or monocrystalline. In particular aspects, crystalline material 132 can be considered to be a silicon seed layer, and crystalline material 134 can be considered to be a second crystalline layer epitaxially grown over the silicon seed layer. In particular aspects, crystalline material 130 can be considered to be a silicon seed layer and 132/134 can be replaced with a second crystalline layer.

Crystalline materials 132 and 134 are oppositely doped relative to source/drain regions 116, and electrical nodes 130 and 136; and in the shown embodiment are doped with p-type dopant. Such doping of materials 132 and 134 can be accomplished by, for example, one or more suitable implants. Crystalline materials 132 and 134 can be doped simultaneously, or sequentially. In a particular aspect, crystalline material 132 is doped prior to formation of material 134; and crystalline material 134 is subsequently doped by out-diffusion from material 132.

Resistor 135 is electrically connected with one of the source/drain regions 116 through conductive pillar 130. In the shown embodiment, one of the crystalline layers 132 and 134 physically contacts conductive pillar 130. It is to be understood, however, that the invention encompasses other aspects (not shown) in which an intervening conductive material is provided between crystalline materials 132 and 134 and conductive pillar 130, as well as other aspects (not shown) in which both of crystalline materials 132 and 134 physically contact conductive pillar 130. Also, it is to be understood that even though only two crystalline layers are shown within the illustrated resistor 135, the invention encompasses other aspects (not shown) wherein more than two crystalline layers are incorporated into a resistor construction.

Both of crystalline materials 132 and 134 of resistor 135 contact electrical node 136. It is to be understood, however, the invention encompasses other aspects (not shown) in which only one of crystalline materials 132 and 134 contacts electrical node 136.

An insulative material (or mass) 140 is over gate 114, and resistor 135 is separated from gate 114 by the insulative material. In the shown embodiment, resistor 135 extends across gate 114, and accordingly a portion of resistor 135 is directly over gate 114. In the shown aspect of the invention, both of crystalline layers 132 and 134 physically contact insulative mass 140; the mass being against an upper surface of material 134 and against a lower surface of material 132.

Construction 100 includes a contact 166 extending from a source/drain region 116, through an opening in resistor 135 (the opening has a periphery 142), and to an interconnect 152 which electrically connects with ground (not shown). Construction 100 also includes a contact 164 (shown in phantom view in FIG. 11 as it is behind the cross-section of FIG. 11). Contact 164 extends to node 136. An interconnect 150 (shown in phantom view in the cross-section of FIG. 11) extends between contact 164 and V_(DD) (not shown in FIG. 11). In particular aspects, node 136 can be considered to be part of the electrical connection to V_(DD).

FIG. 12 illustrates a top view of construction 100, with insulative mass 140 not being shown in FIG. 12 to aid in clarity of the illustration. Gate 114 is part of a conductive line 160, which is connected thorough an electrical stud 162 to other circuitry.

Resistor 135 is shown comprising a “L” shape having an opening extending therethrough for passage of contact 166. Resistor 135 is shown to comprise an outer surface 144, and an inner surface 142. The inner surface 142 defines a periphery of the opening around the contact 166.

FIG. 11 shows various different dopant levels, and utilizes the designations p+, p, p−, n−, n and n+ to distinguish the levels. The difference in dopant concentration between the regions identified as being p+, p, and p− are typically as follows. A p+ region has a dopant concentration of at least about 10²⁰ atoms/cm³, a p region has a dopant concentration of from about 10¹ to about 10¹⁸ atoms/cm³, and a p− region has a dopant concentration in the order of or less than 10¹⁶ atoms/cm³. It is noted that regions identified as being n−, n and n+ will have dopant concentrations similar to those described above relative to the p−, p and p+ regions respectively, except, of course, the n regions will have an opposite-type conductivity enhancing dopant therein than do the p regions.

The p+, p, and p− dopant levels are shown in the drawing only to illustrate differences in dopant concentration. It is noted that the term “p” is utilized herein to refer to both a dopant type and a relative dopant concentration. To aid in interpretation of this specification and the claims that follow, the term “p” is to be understood as referring only to dopant type, and not to a relative dopant concentration, except when it is explicitly stated that the term “p” refers to a relative dopant concentration. Accordingly, for purposes of interpreting this disclosure and the claims that follow, it is to be understood that the term “p-type doped” refers to a dopant type of a region and not a relative dopant level. Thus, a p-type doped region can be doped to any of the p+, p, and p− dopant levels discussed above. Similarly, an n-type doped region can be doped to any of the n+, n, and n− dopant levels discussed above.

FIG. 13 illustrates generally, by way of example, but not by way of limitation, an embodiment of a computer system 400 according to an aspect of the present invention. Computer system 400 includes a monitor 401 or other communication output device, a keyboard 402 or other communication input device, and a motherboard 404. Motherboard 404 can carry a microprocessor 406 or other data processing unit, and at least one memory device 408. Memory device 408 can comprise various aspects of the invention described above, including, for example, the DRAM unit cell described with reference to FIG. 8. Memory device 408 can comprise an array of memory cells, and such array can be coupled with addressing circuitry for accessing individual memory cells in the array. Further, the memory cell array can be coupled to a read circuit for reading data from the memory cells. The addressing and read circuitry can be utilized for conveying information between memory device 408 and processor 406. Such is illustrated in the block diagram of the motherboard 404 shown in FIG. 14. In such block diagram, the addressing circuitry is illustrated as 410 and the read circuitry is illustrated as 412.

In particular aspects of the invention, memory device 408 can correspond to a memory module. For example, single in-line memory modules (SIMMs) and dual in-line memory modules (DIMMs) may be used in the implementation which utilize the teachings of the present invention. The memory device can be incorporated into any of a variety of designs which provide different methods of reading from and writing to memory cells of the device. One such method is the page mode operation. Page mode operations in a DRAM are defined by the method of accessing a row of a memory cell arrays and randomly accessing different columns of the array. Data stored at the row and column intersection can be read and output while that column is accessed.

An alternate type of device is the extended data output (EDO) memory which allows data stored at a memory array address to be available as output after the addressed column has been closed. This memory can increase some communication speeds by allowing shorter access signals without reducing the time in which memory output data is available on a memory bus. Other alternative types of devices include SDRAM, DDR SDRAM, SLDRAM, VRAM and Direct RDRAM, as well as others such as SRAM or Flash memories.

Transistor/resistor constructions of, for example, the type described with reference to FIGS. 11 and 12, can be incorporated into the computer system 400. For instance, a circuit within the computer system can be provided at V_(DD) potential and another circuit can be provided at ground potential. A source/drain region of the transistor can be electrically connected to the circuit at ground potential, and the other source/drain region can be electrically coupled to the resistor which in turn is electrically coupled to V_(DD) potential.

In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents. 

1. A semiconductor construction, comprising: a transistor device having a gate and an active region proximate the gate; the active region comprising a pair of source/drain regions; and a resistor in electrical connection with one of the source/drain regions; the resistor comprising a first crystalline layer and a second crystalline layer over the first crystalline layer; the second crystalline layer having a different composition than the first crystalline layer; the second crystalline layer comprising doped silicon/germanium and the first crystalline layer comprising doped silicon.
 2. The construction of claim 1 wherein the transistor device is comprised by an SOI assembly supported by a substrate.
 3. The construction of claim 2 wherein the substrate comprises a semiconductive material.
 4. The construction of claim 2 wherein the substrate comprises glass.
 5. The construction of claim 2 wherein the substrate comprises aluminum oxide.
 6. The construction of claim 2 wherein the substrate comprises silicon dioxide.
 7. The construction of claim 2 wherein the substrate comprises a metal.
 8. The construction of claim 2 wherein the substrate comprises a plastic.
 9. The construction of claim 1 further comprising an insulative material over the transistor device gate; wherein the resistor is over the insulative material; and wherein at least a portion of the first and second crystalline layers of the resistor is directly over the transistor device gate.
 10. The construction of claim 1 wherein the first crystalline layer consists of doped silicon.
 11. The construction of claim 1 wherein the second crystalline layer comprises from about 10 to about 60 atomic percent germanium.
 12. The construction of claim 1 wherein the second crystalline layer is polycrystalline.
 13. The construction of claim 1 wherein the second crystalline layer is monocrystalline.
 14. The construction of claim 1 wherein the active region extends into a third crystalline layer; the entirety of the active region within the third crystalline layer being within only a single crystal of the third crystalline layer.
 15. The construction of claim 14 wherein the third crystalline layer comprises from about 10 to about 60 atomic percent germanium.
 16. The construction of claim 14 wherein the third crystalline layer is polycrystalline.
 17. The construction of claim 14 wherein the third crystalline layer is monocrystalline.
 18. The construction of claim 14 wherein the third crystalline layer has a relaxed crystalline lattice, and further comprising a strained crystalline lattice layer between the third crystalline layer and the transistor device gate.
 19. The construction of claim 18 wherein the strained crystalline lattice includes silicon.
 20. The construction of claim 18 wherein the strained crystalline lattice includes silicon and germanium.
 21. The construction of claim 14 wherein the transistor device is an NFET device.
 22. A semiconductor construction, comprising: a transistor device having a gate and an active region proximate the gate; the active region comprising a pair of source/drain regions; an electrically insulative mass over the transistor device; an electrically conductive pillar extending upwardly from one of the source/drain regions and through the insulative mass; and a resistor over the insulative mass and in physical contact with the electrically conductive pillar; the resistor comprising a first crystalline layer and a second crystalline layer over the first crystalline layer; the second crystalline layer having a different composition than the first crystalline layer; the second crystalline layer comprising doped silicon/germanium and the first crystalline layer comprising doped silicon.
 23. The construction of claim 22 wherein the source/drain regions comprise a first conductive type; wherein the conductive pillar comprises a semiconductive material conductively doped to the first conductive type; and wherein the first and second crystalline layers of the resistor are conductively doped to a second conductivity type which is opposite the first conductivity type.
 24. The construction of claim 23 wherein the pillar has an uppermost surface, and wherein the first crystalline layer is over the pillar and physically against the uppermost surface of the pillar.
 25. The construction of claim 23 wherein the first conductivity type is n-type and the second conductivity type is p-type.
 26. The construction of claim 23 further comprising a conductive connection to V_(DD); wherein the conductive connection comprises a semiconductive material conductively doped to the first conductivity type; and wherein at least one of the first and second crystalline layers of the resistor physically contacts the conductive connection.
 27. The construction of claim 26 wherein the first conductivity type is n-type and the second conductivity type is p-type.
 28. The construction of claim 26 wherein both of the first and second crystalline layers of the resistor physically contact the conductive connection.
 29. The construction of claim 22 wherein the first crystalline layer is in physical contact with the insulative mass.
 30. The construction of claim 22 wherein the first crystalline layer consists of doped silicon.
 31. The construction of claim 22 wherein the second crystalline layer comprises from about 10 to about 60 atomic percent germanium.
 32. The construction of claim 22 wherein the second crystalline layer is polycrystalline.
 33. The construction of claim 22 wherein the second crystalline layer is monocrystalline.
 34. The construction of claim 22 wherein the active region extends into a third crystalline layer; the entirety of the active region within the third crystalline layer being within only a single crystal of the third crystalline layer.
 35. The construction of claim 34 wherein the third crystalline layer comprises from about 10 to about 60 atomic percent germanium.
 36. The construction of claim 34 wherein the third crystalline layer is polycrystalline.
 37. The construction of claim 34 wherein the third crystalline layer is monocrystalline.
 38. The construction of claim 34 wherein the third crystalline layer has a relaxed crystalline lattice, and further comprising a strained crystalline lattice layer between the third crystalline layer and the transistor device gate.
 39. The construction of claim 38 wherein the strained crystalline lattice includes silicon.
 40. The construction of claim 38 wherein the strained crystalline lattice includes silicon and germanium.
 41. The construction of claim 22 wherein the transistor device is an NFET device. 